textproduct: Rapid City

KEY MESSAGES

- Areas of fog, dense at times, reforming across the northwest and central counties overnight.

- A little cooler for Friday, but warming back up for the weekend and staying dry

DISCUSSION

(This Evening Through Thursday) Issued at 120 PM MST Thu Jan 1 2026

Latest analysis shows western CONUS ridge in place across the Rockies with mild northwest flow in place across the region. Closed 500hpa low spinning onshore across southern CA with next little ripple in 500hpa flow now moving through 500hpa ridge in eastern ID/western WY. At the surface, low pressure is located in south central SD located along cold front that stretches northwest ward into central MT. North of this boundary, temps are in the mid 20s, south of the boundary mid to upper 50s are the rule.

As the aforementioned 500hpa wave traverses through the ridge then drops into the region overnight, it will pull this cold front/boundary further west and south. Low clouds/fog in ND/eastern SD will also ooze to the west as well. Low level condensation pressure deficits...especially across the northern forecast area fall into the 20mb range or less overnight and noticed that ensembles are showing probabilities that visibilities will fall to a mile or less at 50-60% across much of our northern counties. Given that we had dense fog occur this morning, will stick with persistence and plan on it occurring again overnight. A dense fog advisory will be issued from 00z Friday to 15z Friday.

The other issue is the probability of pcpn with the 500hpa wave as it move across mainly NE late tonight into Friday morning. There remains continued 700hpa theta-e forcing associated with this weak wave, and forecast soundings from the southeast forecast area indicates a layer of warm air above the cold air at the surface, leading to the possibility of -fzra, if the column can saturate enough. Have kept inherited low pops for the area.

WAA returns back to the region beginning Friday night and continues through the weekend. Highs will once again be well above seasonal norms as the upper ridge shifts into the central plains. However, there are some signs that colder...not cooler...temps are headed our way toward the end of next week with increasing pcpn chances. Stay tuned.

AVIATION

(For the 06Z TAFS Through 06Z Friday Night) Issued At 1000 PM MST Thu Jan 1 2026

Expect VFR conditions to prevail across northeastern WY, the Black Hills, and southwestern SD through the TAF period. MVFR/IFR/LCL LIFR conditions in low stratus and freezing fog will continue to overspread northwestern into south central SD through tonight, likely reaching the KRAP terminal by around 11z. Conditions should improve late Friday morning into Friday afternoon.

UNR WATCHES/WARNINGS/ADVISORIES

SD...Dense Fog Advisory until 8 AM MST Friday for SDZ001-002-012>014- 032-073-078. WY...None.